1. Field of the Invention
The present invention relates generally to a main housing, and more particularly to a main housing for optical sub-assembly for transceivers.
2. Description of the Related Art
In current optical communication systems, laser diodes are generally used as light sources. A packaged laser diode serves as a laser diode element. A packaged light detector serves as a light detection element. As shown in FIGS. 1 and 2, front end of a laser diode element 1a and front end of a light detection element 2a are respectively connected with two metal fixtures 3 to form a light transmission unit 1 and a light receiving unit 2. Finally, the light transmission unit 1, the light receiving unit 2 and a main housing 4 are fixed and packaged to achieve an optical sub-assembly 5 for transceivers. An optical filter 6 is disposed in the interior of the main housing 4. The upper and lower surfaces of the optical filter 6 are evaporation-coated with mediums of different permeability. The light emitted from the laser diode element 1a is refracted and coupled to an optical fiber 9a via the optic filter 6. The received light is totally reflected to the light detection element 2a through the optical filter 6.
The optical fiber 9a is coaxially arranged in an optical fiber connector 9. The optical fiber connector 9 is placed in a sleeve 11. The sleeve 11 is affixed to the main housing 4 by laser welding.
The optic filter 6 is affixed to a frame 8 of a filter holder 7 and the filter holder 7 is inserted into the main housing 4. A locating pin 10 is inserted between the main housing 4 and the filter holder 7 to locate the optical filter 6 in a fixed angular position. The received/transmitted light can be reflected or refracted by the optical filter 6 and coupled to the optical detection element 2a and the optical fiber 9a. 
In general, the main housing 4 is processed with a miller. It is impossible to directly form a 45-degree holder inside the main housing 4 by means of mechanical processing. Therefore, it is necessary to affix the optical filter 6 to the frame 8 of the filter holder 7 and use the locating pin 10 to lock the filter holder 7 in a fixed position. Accordingly, the optical filter 6 is 45-degree positioned in the main housing 4 to efficiently provide optical coupling effect. Due to the factor of machining of the main housing 4, the filter holder 7 and the locating pin 10, the optical filter 6 can be hardly stably located in the true angular position. As a result, the position of the focal point of the optical filter 6 may be changed to cause loss in performance.